This invention relates to an energy absorber for a motor vehicle steering column.
A typical energy absorbing steering column on a motor vehicle includes a housing or mast jacket which translates linearly through a collapse stroke during a collision of the motor vehicle with another object when a steering hand wheel on the steering column is impacted by the operator of the motor vehicle. The mast jacket translates against a resisting force produced by an energy absorber which converts into work a fraction of the kinetic energy of the operator. Commonly, the resisting force is created by plastic deformation of a metal element of the energy absorber. For example, in the energy absorber described in U.S. Pat. No. 3,392,599, steel spheres plastically deform a metal mast jacket by rolling tracks in the mast jacket. In other prior energy absorbers, a U-shaped or a J-shaped flat metal strap attached to the mast jacket is plastically deformed by being pulled over a stationary convex anvil or vice versa. An energy absorber according to this invention is an improvement relative to prior energy absorbers having plastically deformable flat metal straps in that it includes structural features which contribute to consistently predictable performance of the energy absorber and to simple assembly and installation thereof.
This invention is a new and improved energy absorber for a motor vehicle steering column having a mast jacket supported on a body of the vehicle for linear translation through a collapse stroke in response to an impact on a steering hand wheel on the mast jacket. The energy absorber includes a pair of plastic guides each of which is molded flat and closes at an integral living hinge around a corresponding one of a pair of serpentine flat metal straps so that the straps are captured in the guides between pairs of convex anvils on the guides. Each guide snaps into a guide slot in a mounting bracket on the mast jacket. An inboard end of each flat metal strap is clamped to the vehicle body so that during the collapse stroke of the mast jacket, relative linear translation between the mounting bracket and the serpentine flat metal straps causes each of the straps to be thrust against and pulled across corresponding ones of the convex anvils. Forces attributable to plastic deformation of the flat metal straps at the convex anvils resist linear translation of the mast jacket through its collapse stroke so that a fraction of the kinetic energy of the impact is converted into work. The dimensional accuracy of the molded plastic guides contributes to consistently predictable performance of the energy absorber. Molding the plastic guides flat and closing each around one of the serpentine flat metal straps and then snapping the plastic guides into the guide slots in the mounting bracket simplifies the assembly and installation of the energy absorber for manufacturing economy.